Asteriornis

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Asteriornis
Temporal range: Late
Ma
↓
Skull in lateral view
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Infraclass: Neognathae
Clade: Pangalloanserae
Genus: †Asteriornis
Field et al. 2020
Type species
†Asteriornis maastrichtensis
Field et al. 2020

Asteriornis ("

last common ancestor for both groups.[1][3]

Asteriornis may shed light on why Neornithes were the only

phylogenies[8] and the discovery of Vegavis (a possible neornithean from Antarctica),[9] but Asteriornis's presence in Europe suggests that modern birds may have been widespread in northern continents in their early evolution.[1]

Discovery and naming

Asteriornis is based on specimen NHMM 2013 008, held in the

Eben-Emael in the Maastricht Formation of Belgium,[1] and was first unearthed in 2000,[10] by amateur paleontologist Maarten van Dinther,[11] who donated it to the museum.[1] This geological formation is the namesake of the Maastrichtian stage, which was the last stage of the Cretaceous period and the Mesozoic era. It is dated to around 66.8 to 66.7 million years old,[12] less than a million years before the arrival of the asteroid that caused the Cretaceous–Paleogene extinction event, killed off all non-avian dinosaurs (and many other animals), and began the Cenozoic era.[1]

The genus name, Asteriornis, was constructed from ornis, the

Chicxulub impactor (a "falling star"), and also alludes to quails which are members of the galloanserans. The species name A. maastrichtensis is named after the Maastricht Formation.[1] The researchers who discovered and described the fossil gave Asteriornis the nickname "Wonderchicken", which was picked up by various news outlets.[10][14]

Description

Life restoration

The beak was slightly downcurved and lightweight. Unlike galloanserans, the beak did not have any specialized connections to the rest of the skull, nor a hooked tip. Instead its front tip was slightly rounded. The skull was narrowest over the orbits (eye sockets), where the frontal bones were incised by a V-shaped part of the nasal bones. The bones forming the jaw joint were very galloanseran-like. The quadrate bone (the cranium's contribution to the jaw joint) connected to the skull roof via two pronounced knobs, which were adjacent to a third smaller knob, the tuberculum subcapitulare. The mandible (lower jaw) connected to the quadrate with a pair of sockets, and the rear end of the lower jaw had a large hooked rearward-facing retroarticular process as well as a smaller inward-facing medial process. All of these characteristics are considered unique to (or at least most common in) galloanserans.[1]

In some respects the skull seems more similar to galliform birds such as chickens and pheasants. These include unfused snout bones and nasal bones which fork in front of the eyes. In other respects it resembles anseriform birds such as ducks and geese. Such features include the hooked retroarticular process of the jaw and a postorbital process (the portion of bone forming the rear edge of the eye socket) which curves forward at its lower extent. These demonstrate a principle of evolution that animals close to the common ancestor of two groups share some similarities with each group.[1]

The radius fragment flattens and widens towards the wrist, where it possesses a large hooked bump. Leg bones are elongated and slender, similar in proportions and structure to modern ground-living birds. The femur has well-developed muscle ridges and a large, angular medial condyle. The tibiotarsus is widest towards the knee, while the tarsometatarsus is thinner and covered with ridges.[1]

Classification

A

last common ancestor of chickens and ducks. Bayesian protocol instead placed it within Galloanserae, specifically as the sister taxon to Galliformes. This means that it was more closely related to chickens than to ducks, but also that was not a direct ancestor of modern chicken-like birds.[1]

Classifying Asteriornis as a relative of chickens and ducks means that it is unequivocally a

enantiornitheans, or Archaeopteryx generally resemble modern birds but retain primitive features such as teeth or wing claws.[3] Neornithean fossils are extremely rare from the Mesozoic age, and are generally fragmentary or poorly described. Vegavis from the Late Cretaceous (~66.5 Ma) of Antarctica was originally described as a relative of ducks and geese,[9] but this classification is controversial and some paleontologists do not consider it a proper neornithean.[citation needed] Asteriornis is based on diagnostic and well-preserved skull material and its status is less unstable, so it can be considered the oldest undisputed fossil of a modern-style neornithean bird.[1]

At least one study in 2021 has recovered Asteriornis as a

paleognath, albeit "with limited support".[15] Subsequent studies still support Asterornis as a neornithean closely related to or within Galloanserae based on morphometric and phylogenetic analyses.[16][17]

References

  1. ^
    S2CID 212937591
    .
  2. PMID 24312392
    .
  3. ^
    PMID 32188944
    .
  4. PMID 28973546
    .
  5. PMID 29804807
    .
  6. PMID 27112293
    .
  7. PMID 28696285
    .
  8. PMID 26824065
    .
  9. ^
    S2CID 4354309
    .
  10. ^ a b Giamio, Cara (March 18, 2020). "What to Name the Oldest Modern Bird Fossil? Wonderchicken". The New York Times. Archived from the original on March 19, 2020. Retrieved March 19, 2020.
  11. ^ "Oldest fossil 'Wonderchicken' found at Maastricht by Lab Technician Maarten van Dinther".
  12. ISSN 0016-7746
    .
  13. Perseus Project
    .
  14. ^ KOUMOUNDOUROS, Tessa (March 20, 2020). "This 'Wonderchicken' Could Be The Oldest Modern Bird Fossil, And a True Survivor". ScienceAlert.com. Archived from the original on March 20, 2020. Retrieved March 20, 2020.
  15. PMID 34330706
    .
  16. S2CID 258367829
    .
  17. PMID 38351798
    .
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